POISONOUS SNAKES OF NORTH AMERICA. 391 



attacked, but, in most cases, the victim, after the deadly stroke is given, may still 

 revenge itself by the destruction of the snake. But the certainty of the effect of the 

 poison serves as a warning and is advantageous, not in defense after the attack is 

 made, but in preventing an attack from being made. 



The poiut here made is certainly a strong one, and the theory has 

 been given a fnrther application by the consideration, especially advo- 

 cated by Garman^* that inasninch as the snccess of the snake in cap- 

 ture of food depends on an ever-ready supply of poison, the rattling- 

 sound is advantageous if it keeps away disturbers which can not serve 

 as food and tlius prevents useless expenditure of venom or even the 

 breaking of the fangs. 



If we now look at the various explanations given, it seems possible 

 to accept them all as partly true. The rattle having once been 

 acquired it seems even probable that the snake used the sound for the 

 various purposes indicated, though of course it may be difficult to 

 point out which one has mostly influenced the evolution of the instru- 

 ment. To me the rattling appears as a substitute for a voice, and I 

 think it is quite logical to conclude that it may be put advantageously 

 to all the uses to which an animal may apply its voice. 



It has long been known that most snakes when agitated produce a 

 whirring or rustling sound, which often strongly resembles the noise 

 of the Eattlesnake,by rajndly vibrating the end of the tail among dead 

 leaves, or against some other object, even their own body. Many an 

 innocent snake has, on tliis account, suffered an untimely death, having 

 been mistaken for the deadly rattler. This fact has been used as an 

 argument in favor of the preventive theory, since, if the rattling is 

 advantageous to the rattlesnake in preventing attack by its enemies, 

 the imitation of the noise must also prove advantageous to the mim- 

 ickers. The fact that this pseudo-rattling is indulged in by the deadly 

 snakes without a rattle does not mitigate against this theory of imita- 

 tion, for of course, if it is advantageous to the rattlesnake to have a 

 means of preventing unneccessary waste of poison or useless exposure 

 to breakage of the fangs, the imitation must be equally advantageous 

 to the Copperhead or the Moccasin. But the futility of the theorj^ is 

 shown not only in the fLictthat this vibration of the tail is so universal, 

 but still more so because it does not seem to be confined to the snakes 

 of America, to which part of the world the Rattlesnakes are restricted. 



It is evident, then, that this vibrating of the tail, so tar from being an 

 imitation of the rattlesnake's way of making itself heard, was a common 

 characteristic of most snakes before' the Rattlesnake evolved from the 

 common ancestral stock of Pit Vipers. Whatever the cause of this 

 phenomenon — and we may well accept Herbert Spencer's suggestion, 

 as applied by Shaler (oj?. cit., p. 3G), that the wagging of the dog's tail 

 and similar movements of that appendage is an escape of nervous force 

 restrained from other modes of expression at the moment — we may take 



*Ophid. N. Araer., 1883, p. xxvi; Bull. Mus. Com. Zool., xiii, 1888, p. 264. 



